Media Termination Points

A Media Termination Point (MTP) software device allows the Cisco CallManager to extend supplementary services, such as hold and transfer, to calls that are routed through an H.323 endpoint or an H.323 gateway.

Understanding Media Termination Points

The MTP accepts two full-duplex G.711 Coder-Decoder (CODEC) stream connections. MTPs bridge the media streams between two connections. The streaming data that is received from the input stream on one connection passes to the output stream on the other connection and vice versa. In addition, the MTP trancodes a-law to mu-law (and vice versa) and adjusts packet sizes as required by the two connections.

MTPs extend supplementary services, such as call hold, call transfer, call park, and conferencing, that are otherwise not available when a call is routed to an H.323 endpoint. Some H.323 gateways may require that calls use an MTP to enable supplementary call services, but normally, Cisco IOS gateways do not.

Each MTP belongs to a device pool, which specifies, in priority order, the list of Cisco CallManagers to which the devices that are members of the device pool should attempt to register. This list represents a Cisco CallManager group. The first Cisco CallManager in the list specifies a device primary Cisco CallManager.

An MTP device always registers with its primary Cisco CallManager if that Cisco CallManager is available and informs the Cisco CallManager about how many MTP resources it supports. The Cisco CallManager controls MTP resources. You can register multiple MTPs with the same Cisco CallManager. When more than one MTP is registered with a given Cisco CallManager, that Cisco CallManager controls the set of resources for each MTP. You can also distribute the MTPs across a networked system as desired.

For example, MTP server 1 is configured for 48 MTP resources. The MTP server 2 is configured for 24 resources. If both MTPs register with the same Cisco CallManager, that Cisco CallManager maintains both sets of resources for a total of 72 registered MTP resources.

When the Cisco CallManager determines that a call endpoint requires an MTP, it allocates an MTP resource from the MTP that has the least active streams. That MTP resource gets inserted into the call on behalf of the endpoint. MTP resource use remains invisible to both the users of the system and to the endpoint on whose behalf it was inserted. If an MTP resource is not available when it is needed, the call connects without using an MTP resource, and that call does not have supplementary services.

Make sure that the Cisco IP Voice Media Streaming application is activated and running on the server on which the MTP device is configured.

The Cisco IP Voice Media Streaming application, which is common to the MTP, Conference Bridge, and Music On Hold applications, runs as a Windows 2000 service.

•You can manually install the Cisco IP Voice Media Streaming Application on a networked server and configure an MTP device on that server through Cisco CallManager Administration.

Managing MTPs with the Media Resource Manager

The Media Resource Manager (MRM), a software component in the Cisco CallManager system, primarily functions for resource registration and resource reservation. Each MTP device that is defined in the database registers with the MRM. The MRM keeps track of the total available MTP devices in the system and of which devices have available resources.

During resource reservation, the MRM determines the number of resources, identifies the media type (in this case, the MTP), and the location of the registered MTP device. The MRM updates its shared resource table with the registration information and propagates the registered information to the other Cisco CallManagers within the cluster.

The MRM enhances the Cisco CallManager MTP, Music On Hold, Conference Bridge, and Transcoder devices by distributing the resources throughout the CallManager cluster, making the features more efficient and economical.

MRM also supports the coexistence of an MTP and transcoder within a Cisco CallManager.

Planning Your MTP Configuration

Consider the following information when you are planning your MTP configuration:

•An improper setting can result in undesirable performance if the workload is too high.

•A single MTP provides a default of 48 MTP (user configurable) resources, depending on the speed of the network and the network interface card (NIC). For example, a 100-MB Network/NIC card can support 48 MTP resources, while a 10-MB NIC card cannot.

•For a 10-MB Network/NIC card, approximately 24 MTP resources can be provided; however, the exact number of MTP resources that are available depends on the amount of resources that is being consumed by other applications on that PC, the speed of the processor, network loading, and various other factors.

Consider the following formula to determine the approximate number of MTPs that are needed for your system, assuming that your server can handle 48 MTP resources (you can substitute 48 for the correct number of MTP resources that are supported by your system):

A number divided by 48 = number of MTP applications needed (n/48 = number of MTP applications).

where:

n represents the number of H.323 devices that require MTP support.

If a remainder exists, add another server with Cisco IP Voice Streaming Application server with MTP.

•If one H.323 endpoint requires an MTP, it consumes one MTP resource. Depending on the originating and terminating device type, a given call might consume more than one MTP resource. The MTP resources that are assigned to the call get released when the call terminates.

•Use Performance Monitor to monitor the usage of MTP resources. The Performance Monitor counter, Media TermPoints Out of Resources, increments for each H.323 call that connects without an MTP resource when one was required. This number can assist you in determining how many MTP resources are required for your callers, and whether you have adequate coverage.

•Identical system requirements apply for the Cisco IP Voice Media Streaming Application and MTP and the Cisco CallManager system.

MTP Device Characteristics

The Full Streaming Endpoint Duplex Count, a number of MTP resources that are supported by a specific MTP, represents a device characteristic that is specific to MTP device configuration. Refer to the "Media Termination Point Configuration Settings" section in the Cisco CallManager Administration Guide for a detailed description of all MTP device settings.

Avoiding Call Failure/User Alert

To prevent call failure or user alert, avoid the following conditions:

•Although the Cisco IP Voice Media Streaming Application service can run on the same PC as the Cisco CallManager, we strongly recommend against this. If the Cisco IP Voice Media Streaming Application is running on the same PC as the Cisco CallManager, it can adversely affect the performance of the Cisco CallManager.

•When you configure the MTP, a prompt asks you to reset MTP before any changes can take effect. This action does not result in disconnection of any calls that are connected to MTP resources. If you choose Reset, as soon as the MTP has no active calls, the changes take effect.

Note When you make updates to the MTP and you choose Restart, all calls that are connected to the MTP get dropped.

MTP System Requirements and Limitations

The following system requirements and limitations apply to MTP devices:

•You can activate only one Cisco IP Voice Streaming Application per server. To provide more MTP resources, you can activate the Cisco IP Voice Streaming application on additional networked Windows NT servers.

•Each MTP can register with only one Cisco CallManager at a time. The system may have multiple MTPs, each of which may be registered to one Cisco CallManager, depending on how your system is configured.

•Cisco strongly recommends that you do not activate the Cisco IP Voice Streaming Media Application on a Cisco CallManager with a high call-processing load because it can adversely affect the performance of the Cisco CallManager.

MTP Failover and Failback

This section describes how MTP devices failover and failback when the Cisco CallManager to which they are registered becomes unreachable. This section also explains conditions that can affect calls that are associated with an MTP device, such as MTP reset or restart.

Active Cisco CallManager Becomes Inactive

The following description gives the MTP device recovery methods when the MTP is registered to a Cisco CallManager that goes inactive:

•If the primary Cisco CallManager fails, the MTP attempts to register with the next available Cisco CallManager in the Cisco CallManager Group that is specified for the device pool to which the MTP belongs.

•The MTP device reregisters with the primary Cisco CallManager as soon as it becomes available after a failure and is currently not in use.

•The system maintains the calls or conferences that were active in call preservation mode until all parties disconnect. The system does not make supplementary services available.

•If an MTP attempts to register with a new Cisco CallManager and the register acknowledgment is never received, the MTP registers with the next Cisco CallManager.

Resetting Registered MTP Devices

The MTP devices will unregister and then disconnect after a hard or soft reset. After the reset completes, the devices reregister with the Cisco CallManager.